# Instructing People to use minnimum time for a task? [duplicate]

There are 5 persons standing on a side of tunnel.

A, B, C, D, E


Each takes 10, 30, 15, 20, 29 minutes to cross tunnel respectively.

You are giving them instructions to cross.

Problem is at a time 2 person can cross tunnel with flash light.

After crossing one person should come back with flash light because its only one.

How you will manage them so that in a minimum time they can cross tunnel?

The following sequence should be optimal:

Step 1: A & C to cross. Time elapsed, 15 mins.
Step 2: A to return. Time elapsed, 25 mins.
Step 3: B & E to cross. Time elapsed, 55 mins.
Step 4: C to return. Time elapsed, 70 mins.
Step 5: A & D to cross. Time elapsed, 90 mins.
Step 6: A to return. Time elapsed, 100 mins.
Step 7: A & C to cross. Time elapsed, 115 mins. All crossed.